1. Field of the Invention
This invention relates to isolation technology and more particularly to isolators providing isolation between a control signal and a driver circuit.
2. Description of the Related Art
Opto-isolators have been used with driver circuits to provide isolation between the control signal and the drivers. An example of a traditional opto-isolator is shown in FIG. 1. When a current on node 101 is applied to light emitting diode (LED) 103, the diode emits light which is received by photo transistor 105. FIG. 1 also shows a high voltage driver 107. The voltage of the high voltage driver is typically 12-25 volts, but may be higher, depending on the application. When the current is supplied on node 101, the driver 107 turns on.
One problem with the opto-isolators shown in FIG. 1 is that the output of the diode is dependent on the strength of the current. That is, the harder the diode is driven, the stronger the diode output. Thus, switching characteristics may be undesirable. In addition, opto-drivers may be susceptible to common mode input transients and so an external resistor 111 may be chosen to overdrive the LED 103 to keep it on when a common mode transient occurs during an output high state. However, that causes less efficiency during operation when the control current is turned off via control transistor 112 due to the dissipation through external resistor 111.
Thus, it would be desirable to provide improved isolation technology with greater immunity to input common mode transients and improved operating efficiency.